Pass -mtls-use-call when building libraries used in IRT.

src/shared/platform/nacl.scons

Index: src/shared/platform/nacl.scons
diff --git a/src/shared/platform/nacl.scons b/src/shared/platform/nacl.scons
index 2557c6c1c5857a7c4c6f8e4b07be4676e8f79c49..a832503573fee327d3b90dcb208920b82e2da051 100644
--- a/src/shared/platform/nacl.scons
+++ b/src/shared/platform/nacl.scons
@@ -1,11 +1,19 @@
 # -*- python -*-
-# Copyright 2010 The Native Client Authors.  All rights reserved.
-# Use of this source code is governed by a BSD-style license that can
-# be found in the LICENSE file.
+# Copyright (c) 2011 The Native Client Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 
 Import('env')
 env.Append(CCFLAGS=['-Wno-long-long'])
 
+# This library is linked into irt.nexe (see src/untrusted/irt/).
+# All IRT code must avoid direct use of the TLS ABI register, which
+# is reserved for user TLS.  Instead, ensure all TLS accesses use a
+# call to __nacl_read_tp, which the IRT code overrides to segregate
+# IRT-private TLS from user TLS.
+if not env.Bit('bitcode'):
+  env.Append(CCFLAGS=['-mtls-use-call'])
+
 platform_inputs = [
     'nacl_check.c',
     'nacl_log.c',